Long neck (steamer) clams, Lobster, corn on the cob, white potatoes, clam broth, melted butter. I figure steaming it in a bed of seaweed takes care of the green vegetable requirement.
Nutritional value? Really? One does not approach a clam bake with nutritional concerns because it's a feast. But, for the sake of completeness, here are some notional values. [I say 'notional' because the serving sizes are risible... one cup of clam meat? Dude! That's just an appetizer serving!!]
A clambake does not make for a good daily diet. It's high in fat (butter is a necessary component, but the serving size is left to the individual); high in cholesterol; high in protein; not a bonanza for vitamins; high in iodine and some other minerals.